Internal combustion engines function by the combustion of fuels which in turn generate the power needed to propel vehicles. In the case of a diesel engine, the fuel is a diesel fuel and the combustion thereof generally results in emissions from the exhausts of such vehicles which comprise three main components: soot and particulate matter, carbon monoxide and nitrogen oxides (NOx). To alleviate environmental concerns, research is ongoing to reduce the levels of these emissions. NOx emissions can be reduced by lowering the temperature at which the fuel is combusted in the engine. Typically, this is achieved by retarding the combustion, i.e., by injecting the fuel shortly after the peak temperature is reached in the cylinder. However, this retarded combustion has the disadvantage that it causes more soot to accumulate in the engine lubricant partly due to incomplete combustion of the fuel because of the lower combustion temperature, and partly due to increased soot deposition on the cylinder wall which is drawn down into the lubricant with the downward stroke of the piston. The presence of soot in the lubricant has the adverse effect of causing viscosity increase and accelerated wear. It is important that soot induced viscosity increase be controlled such that the lubricant stays within viscosity grade in order to maintain its expected performance and to enable quick and clean drainage of the engine during servicing.
Lubricating oil compositions comprise a major amount of base oil and additives that improve the performance and increase the useful life of the lubricant. Nitrogen-containing dispersants are commonly used lubricant additives. The function of a dispersant is to maintain in suspension within the oil, insoluble materials formed by oxidation and other mechanisms during use of the oil, to prevent sludge flocculation and precipitation of the insoluble materials. Another function of the dispersant is to reduce the agglomeration of soot particles, thus reducing increases in the viscosity of the lubricating oil upon use. In the severe environment of diesel engines, it has been found that soot induced viscosity increase cannot be controlled by conventional dispersants, even when the amounts of such conventional dispersants are increased. Therefore, compounds providing potent soot dispersing properties and crankcase lubricants providing improved soot dispersing performance are continuously demanded.
The present disclosure provides a dispersant having improved performance in engine tests, providing a good viscosity index and good soot dispersion and toleration properties, particularly in diesel engines, and especially in heavy duty diesel engines employing exhaust gas recirculation.